The present invention relates to a method for controlling a work machine during operation in a repeated work cycle.
The term “work machine” comprises different types of material handling vehicles like construction machines, such as a wheel loader and a dump truck (such as an articulated hauler). A work machine is provided with a bucket, container or other type of work implement for carrying/transporting a load. Further terms frequently used for work machines are “earth-moving machinery” and “off-road work machines”.
In connection with transportation of heavy loads, e.g. in contracting work, work machines are frequently used. A work machine may be operated with large and heavy loads in areas where there are no roads, for example for transports in connection with road or tunnel building, sand pits, mines and similar environments.
The term work cycle comprises a route of the work machine (ie the work cycle travel path) and/or a movement of the work implement (lifting/lowering operation). During the performance of the work cycle, the work machine often encounters different gradients of the ground (uphill and downhill), and turns (cornering).
According to a first work cycle example, a wheel loader typically drives into a heap of material, lifts the bucket, reverses out of the heap, turns and is forwarded towards a dump truck where it unloads the material onto the container of the dump truck. After unloading, the wheel loader returns to the starting position.
According to a second work cycle example, a dump truck is loaded at a first position, driven along a varied route, unloaded at a second position and driven back along the varied route. Normally, an excavator or wheel loader loads the container of the dump truck at the first position.
WO 2005/028926 discloses a method for automatically selecting a specific gear mode from a plurality of gear modes on the basis of the type of work cycle that the vehicle currently performs. The vehicle gear box is controlled in response to the selected gear mode. The type of work cycle is determined by detecting a total distance the vehicle is driven in an individual sequence with one of a forward gear position and a reverse gear position.
It is desirable to reduce fuel consumption and/or increase productivity, ie transporting as much material in as short time as possible in a cost-efficient way. Further, the transportation should preferably be performed with due regard to environmental factors.
According to an aspect of the present invention, a method is provided for controlling a work machine during operation in a repeated work cycle comprising the step of controlling the work machine in response to a predetermined control strategy that is based on at least one condition that varies in the course of the work cycle.
The condition which varies may regard for example a work machine behaviour, a work cycle travel path direction and/or a work implement operation. More specifically, the condition variation may comprise a predicted and/or experienced sequence of events that takes place during performance of the work cycle and which is relevant for the control of the work machine. Each such event represents an important change in a work machine operational parameter, and each event is preferably associated to a position along the work cycle travel path.
According to a preferred embodiment, the method comprises the step of establishing the control strategy on the basis of said at least one condition that varies in the course of the work cycle. Thus, the control strategy (or control model) is built up on the basis of the condition variation. The condition variation is associated to a variation in the work machine operational characteristics. In other words, the sequence of events is built up in response to the predicted and/or experienced driving pattern along the work cycle route.
According to a further development of the last mentioned embodiment, the control strategy is based on a condition that varies between end positions of the work cycle. A first of said end positions preferably comprises a loading position and a second of said end positions preferably comprises an unloading position for the work machine.
According to a further preferred embodiment, the method comprises the step of detecting at least one operational parameter during operation of a work machine in the work cycle in question, and establishing at least part of the control strategy on the basis of a magnitude of the detected operational parameter. Preferably, the method comprises the step of repeatedly detecting said at least one operational parameter. Further, a plurality of operational parameters are preferably detected, such as an operational parameter indicative of the work machine weight, an operational parameter indicative of an end position of the work cycle, an operational parameter indicative of a rolling resistance, an operational parameter indicative of a resistance to ground inclination, an operational-parameter indicative of the speed of the work machine and a change of direction of the work cycle travel path. Said at least one operational parameter is preferably substantially continuously repeatedly detected.
Thus, an event may be established on the basis of the detected operational parameter in a previously performed work cycle and used for controlling a work machine by means of the control strategy in a later performed work cycle. More particularly, an individual work machine may be adapted to learn from past experiences.
According to a further preferred embodiment, the method comprises the step of predicting at least part of the condition variation on the basis of pre-available information of the work cycle in question. Such information may be formed by geographical maps of the area covering the work cycle travel path, knowledge of the specific work cycle travel path (comprising turns and slopes), the material to be transported, ground conditions, weather conditions etc. For example, a satellite based system (such as the GPS) may be used for establishing the work cycle travel path.
According to a further preferred embodiment, the control strategy is established on the basis of both detected operational parameters while performing the work cycle and available information of the work cycle in question.
Thus, the work cycle route may be indicated in a topographical map, wherein turns and slopes are defined.
The control strategy is based on such a topographical map and it may be modified based on detected operational conditions such as rolling resistance etc.
Further, the condition variation, such as the work machine behaviour, may differ when the work cycle is performed depending on for example the type, size, condition and weight of the work machine. More specifically, the weight differs substantially in a loaded condition and an unloaded condition. For example, an articulated hauler may have a weight in the order of 15-30 metric tons and may be loaded with a payload in the order of 20-35 tons. Further, different models of a work machine may react differently when the work cycle is performed. Further, different individuals in a fleet may be of different age and have different operation history with a resulting wear in response thereto etc.
Such variations may be taken into account when establishing the control strategy for an individual work machine.
According to a further preferred embodiment, the control strategy comprises a plurality of control steps, wherein each step is established on the basis of the condition variation. Preferably, the work cycle travel path comprises a plurality of positions, wherein each position is established on the basis of the condition variation.
Each control step indicates that the work machine should be effected for an optimum control. Such a control step may be indicated by the position of a change in altitude, or a change in direction, of the work cycle travel path. Further, such a control step may be indicated by the position of a change of the ground conditions (with regard to rolling resistance and/or grip, ie hard versus slippery surface). Further, such a control step may be effected by a total weight of the work machine (comprising any transported material).
According to a preferred embodiment, the method comprises the step of controlling at least one device in a work machine power transmission system in response to the established control strategy during operation of the work machine in the work cycle. Especially, the control strategy comprises work machine powertrain operating information and the method comprising the step of controlling a powertrain component. The term “powertrain” comprises the system for moving the work machine from (and including) a power source (such as a diesel engine) to the ground engaging members (such as wheels).
According to a further preferred embodiment, the control strategy comprises information regarding gear selection and the method comprising the step of controlling a transmission. Preferably, the control strategy comprises information regarding selection of a gear mode from a plurality of gear modes and the method comprising the step of controlling a transmission.
Thus, for a work machine with an automatic gearbox a so-called gear mode or gear function is automatically selected in response to the established control strategy. The gear modes may differ in that changing to a higher gear, changing up, is carried out at different minimum engine speeds, for changing between corresponding gears, and changing to a lower gear is carried out at different minimum vehicle speeds. By automatically controlling the gearbox in response to the established sequence of control events, fuel efficiency can be improved. Further, wear on the transmission can be reduced.
According to a further preferred embodiment, the control strategy comprises information regarding a differential gear operation and the method comprising the step of controlling the differential gear. An articulated hauler comprises a longitudinal and/or transverse differential gear with an associated differential gear lock mechanism. Such differential gear lock mechanisms are used to increase the off road driveability, but they are often engaged also when they are not needed. By automatically controlling the activation of the differential gear lock mechanisms in response to the established sequence of control events, fuel efficiency can be improved and less wear on the components can be achieved, leading to a longer life.
Other advantageous embodiments of the invention and its associated advantages are apparent from the following description.